In-use product and material stocks are now an essential component of cities and urban ecosystem. They refer to the amount of concerned manufactured products and materials in active use. This study estimates the dynamic in-use stocks of various steel-containing products and steel in the city of Xiamen, China, during 1980-2015 by applying a bottom-up accounting approach. We incorporate 55 categories of steel-containing products that are classified into five main end-use sectors (i.e., buildings, infrastructure, transportation equipment, machinery, and domestic appliances). We find that in-use stocks of more than half of the studied products kept increasing during the period 1980-2015, especially after 2000. Steel stocks in Xiamen have grown up to 4.9 ± 1.4 tons per capita (t/cap) in 2015, from 0.5 ± 0.2 t/cap in 1980. Buildings are the largest reservoirs during the studied period, although its share decreased from 89% in 1980 to 68% in 2015. The dynamic spatial distribution indicates that in-use steel stocks gradually expanded from urban core to the suburban areas during the studied period. Results of this study help to explore how a city’s urbanization is sustained by the growth of in-use product and steel stocks in China that has been quickly urbanized. In-use steel stocks, of which the growth is highly correlated to and probably driven by the population growth, GDP increase, and urban built-up area expansion in Xiamen, may serve as a supplementary indicator for urbanization.